2.8 select and deselect like in 2.79
UPD: since beta release were is a setting in settings called select all toggles:



You can just click on this, instead changing shortcuts manually:

Old answer:

Yes. All hotkeys are fully customizable.

Open user preferences, Input tab. You can search hotkeys by key-binding("A"):



There are many different "selects" here for different types of editors and modes. You can change everywere, or in specific part.

In every hotkey you should change an action to toggle:  



After edit hotkeys, don't forget to save user settings.